The present invention relates to a sintering plant of the type sintering pulverized ores while they are continuously fed at one end of an endless conveyor and transported to the other end thereof.
In order to reduce the steel production costs, there have been long used as the raw materials the sintered concentrates obtained by sintering pulverized iron ores which are inexpensive. However, dust and SO.sub.x are contained in large quantities in the gases discharged from the sintering plants so that the various pollution control standards are enforced so that air cleaning equipments such as dust collectors, desulfurization equipment and so on must be installed in the sintering plants, thereby to prevent contamination of the atmosphere. Installation costs of such pollution control equipments are exceedingly expensive and in general three times as high as the capital costs of the sintering plant proper. In addition, the operation costs of these pollution control equipments are also expensive. As a result, the steel production costs cannot be reduced and remain high.
In order to overcome the above and other problems encountered in the sintering plants, there have been made various proposals such as improvements of individual equipments such as dust collectors, desulfurization equipment, etc., but none has yet been particularly successful.
Meanwhile, there has been proposed a method in which only part of the discharged gases containing especially SO.sub.x in large quantities are fed into the desulfurization equipment in order to make it small in size, thereby reducing the capital, operation and other costs. According to the proposed method, an array of wind boxes is disposed below the conveyor for supplying air over the pulverized iron ores being transported and sucking the gases generated when the iron-ores are sintered. In this case, the gases with high SO.sub.x concentrations are discharged from the intermediate wind boxes between the feed and discharge ends. Therefore there has been proposed a method for feeding only the gases discharged from the intermediate wind boxes into a desulfurization equipment. However, in practice, the temperatures of the discharged gases are relatively low so that SO.sub.x become mists in the succeeding stage such as a dust collector disposed immediately upstream of the desulfurization equipment. Therefore it follows that some means must be provided so as to prevent the temperature drop of the discharged gases. In addition, it is difficult to select the wind boxes from which the gases with higher SO.sub. x concentrations are discharged. If the number of the selected wind boxes is large, the capacity of the desulfurization equipment must be increased accordingly. On the other hand, when the number of selected wind boxes is too small, the gases which are discharged without being desulfurized would contain SO.sub.x in certain quantities.
In order to overcome these problems, as disclosed in Japanese Patent Laid Open No. 20904/79, the inventor has proposed a method in which quicklime and water are added to the lower layer of raw materials being transported by the conveyor so that SO.sub.x are generated only in the last half of the sintering process and gases discharged only through the downstream half of a wind box array are fed into the desulfurization equipment. This method has succeeded in eliminating almost all SO.sub.x discharged from the sintering machine with the desulfurization equipment with a relatively low capacity. However, this method has a problem that since the temperatures of the gases discharged from the downstream half of the wind box array are higher than an allowable temperature of the desulfurization equipment, they must be cooled before they are fed into the equipment. More specifically, with a desulfurization equipment of stack gas by active carbon with moving layer method, active carbon particles would be burned if high temperature gases are fed. Thus, the temperatures of the gases fed into the desulfurization equipment must be less than 220.degree. C. at the maximum. With the desulfurization equipment of the wet type using lime and gypsum, satisfactory results cannot be attained unless the gases to be fed are cooled below 60.degree. C. In addition, because of the complicated drain treatments, the desulfurization equipment of the wet type described cannot be used in combination with the sintering plant of the type described.
Obviously, the iron manufacturing plants consume the thermal energy in large quantities so that the improvement of thermal efficiency is essential for increasing the productivity. Therefore it follows that the above-described method in which the discharged gases are cooled before they are fed into the desulfurization equipment results in nothing but waste of still valuable thermal energy. As a result, the thermal efficiency drops and this demerit cancels the merit obtained by making the desulfurization equipment compact in size.